Thoughts on the current Thornmail
Personaly I feel that it's in a really strange position right now. It suppose to be an item that helps vs adc damage but current the power curve more depends on the champion rather than an actualy power item.
Champions that gain bonus armor from abilties 
benefit a lot from the new thornmail. I think it's in the good direction but to give an example for Rammus. 40 extra reflect damage just by pressing a key is big.
Can't we reduce the scaling to something like 10-20% but let it aply Grievous Wounds to compensate?
